Nanosecond-pulsed volume DBD plasma in saturated humid air: a combined experimental and computational study using EFISH and LIF

This study presents a detailed investigation of a nanosecond-pulsed volume dielectric barrier discharge (VDBD) plasma in saturated humid air at atmospheric pressure, combining experimental diagnostics with kinetic modeling. Electric field-induced second harmonic generation (EFISH), employing a spatial filter and a picosecond laser, enabled electric field measurements with high spatial (270 µm) and temporal (28 ps) resolution at three distinct positions across the inter-electrode VDBD gap. These measurements revealed previously unobserved features and consistent differences between the discharge center and regions near the ground and high-voltage (HV) electrodes. Near the ground electrode, a higher electric field was observed prior to the first positive plasma discharge, along with an overshoot up to 50 kV cm−1 during plasma breakdown, absent at the center and near the HV electrode. A sharper post-breakdown decrease and recovery in the electric field was also observed near the ground electrode, differently from the other positions. This pattern inverted during the subsequent negative discharge at the end of the HV pulse, with the higher electric field being measured near the HV electrode. To complement the electric field data, the concentrations of nitric oxide (NO) and hydroxyl radical (OH) were measured using laser-induced fluorescence (LIF), providing insight into their temporal dynamics during and after the discharge. The EFISH data served as input for a zero-dimensional kinetic model, which revealed the dynamics of both charged and neutral species, showing excellent agreement with the LIF data and validating the model accuracy. The simulation identified OH−, O2-, and O4- as the key negative ions responsible for the stable electric field after plasma breakdown. This research highlights the importance of understanding electric field dynamics and reactive species formation in low-temperature plasmas. Integrating EFISH and LIF data with kinetic modeling provides a robust framework to optimize plasma-based systems, improving their performance and safety in practical applications.